A Fuel cell generating electricity from electrochemical reactions of gases has a high power generation efficiency and an extremely small impact on the environment since the discharged gas is clean. Among these, the proton-exchange membrane fuel cell is capable of operating at relatively low temperatures and has a large output density. For this reason, its application to various fields such as power generation and as a power source for automobiles is anticipated.
In the proton-exchange membrane fuel cell, a cell in which separators sandwich a membrane electrode assembly (MEA) or the like serves as the unit of power generation. The MEA is formed from a polymer membrane (electrolyte membrane) acting as an electrolyte, and a pair of electrode catalyst layers (a fuel electrode (anode) catalyst layer and an oxygen electrode (cathode) catalyst layer) respectively arranged on both sides of the electrolyte membrane in the thickness direction. On the surfaces of the pair of electrode catalyst layers a gas diffusion layer is further disposed. Fuel gas such as hydrogen is supplied to the fuel electrode side, while an oxidizing gas such as oxygen and air is supplied to the oxygen electrode side. The supplied gas, the electrolyte, and the electrode catalyst layers are subjected to an electrochemical reaction at the three-phase boundary to generate electricity. The proton-exchange membrane fuel cell is structured by sandwiching a cell stack in which a plurality of the above cells are stacked together between end plates or the like disposed on both ends of the fuel cell in the cell stacking direction.
A manifold serving as a flow path for gas or water is formed on the peripheral edge portion of the cell stack. Mixing of the gases supplied to the respective electrodes creates issues such as lowered power generation efficiency. Also, the electrolyte membrane exhibits proton conductance in a state with water contained therein. Therefore, during operation the electrolyte must maintain a wet state. Accordingly, in order to prevent gas mixing and leakage, as well as maintain a wet state within the cells, a seal member is disposed on the peripheral edge portion of the manifold and the MEA (see Japanese Patent Application Publication Nos. JP-A-2008-123883, JP-W-2001-510932, and JP-A-2005-47262 for examples).